(1) Field of the Invention
The present invention is directed to a process for casting seal slots in turbine engine components, such as turbine vane shrouds, and to a cast turbine engine component having seal slots for improving the sealing mechanisms in the turbine engine component and thereby minimizing leakage from the flow path out through the vane shrouds.
(2) Background
In order to avoid the large thermally induced hoop stresses in outer and inner shrouds of full hoop turbine vane rings, vanes are typically cast and machined as separate segments, containing two or more airfoils, with feather seals installed in slots along the vane shrouds in order to minimize the leakage between the segments. When the use of a continuous vane ring is possible, the inner or outer shrouds may be sliced between the airfoils at regular intervals during the final machining operations, or cast with a slip joint which allows for relative motion between the one end of the vane and the mating shroud. In a full vane ring configuration, the incorporation of feather seals is not practical due to the lack of access to the side faces, or the long cycle times, complexity, and high cost of producing a feather seal slot using an EDM process (plunging the electrode from one of the axial surfaces).
The ability to produce the shroud gaps and the imbedded seal slots as an as-cast feature could provide significant lead-time and cost reductions. In addition, a cast slot will have a better surface finish than one produced by EDM, which would also contribute to minimizing leakage.
The use of ceramic cores to cast a seal slot in the shroud of a typical vane ring would not produce much success. The small, thin size required for both the main body of the core and any locating or holding feature would not result in sufficient strength to produce acceptable casting yields.